7.COMPUTER CONTROLLED MACHINING
This week we learned how to use software and computer-controlled machinery to automate manufacturing processes
Group assignment:
GROUP ASSIGNMENT
You can view our group assignment here!
INDIVIDUAL ASSIGNMENT
Make something big!
We were instructed to use Shopbot as our choice of machine and 8x4 plywood(18mm/12mm) as the material on which we will make the product
Design
It took me a long while to figure out what to make. I have had prior experience in woodworking but that was mostly manual work. Using a CA machine to work on a project was new to me and it was quite challenging. There were some limitations to what designs we could make from the machine such as time taken to create a piece and the dimensional constraints. Initially i was planning to make something with a lot of curved surfaces but i did not go ahead with that since the risk of the furniture breaking were quite high. I wasn't as satisfied at first with the kind of design i was going for but was content as i went on to make more customizations to the design. I went on to design a bookshelf as i wanted one to store my books, knickknacks and display music albums. I wanted the shelf to have some interlocking parts that would fit together like a puzzle. I also wanted the shelves to be open rather than just making a box.
3DModel
This was the most frustrating and challenging part in the entire process for me. I had to make the entire shelf as a parametric design. Even though the design was simple enough adding constraints and variables took me a tedious amount of time to figure out. This was the first time i was trying to make the the entire furniture using parameters. Adding to that my shelf contained a lot of parts that were made to enhance the locking and the looks. As this is to be cut by the machine there wasn't any room for random errors. There were many many many changes that were gone through over and over again which made me feel defeated almost. Each time the model almost came together there was one small component causing a headache that would require me to completely dismantle the model and build it again. Thankfully, my peers and instructors were extremely helpful and guided me through every roadblock. There are still some issues that im trying to resolve where some of the parameters are not working properly. But as i am on limited time i had to move on after making an acceptable model where the thickness can be controlled which is the main requirement for cutting on the machine.
Cardboard Mockup
I was quite satisfied with the fit and held up better than i thought while modelling.
I also was able to figure out how to assemble the parts efficiently as well.
Preparing the Job
Before taking the plywood to the machine ,we need to check the thickness of the piece as it will affect the overall
dimensions of the furniture. I measred the thickness of the plywood with a vernier calliper and found out that the
average thickness of the piece i was given was 17.2mm.
As i had made the model with a thickness of 18mm i had to change the scale of the model.
I also had to take into account the offset value from the machine that turned out to be 0.2mm ,
which we concluded in the group assignment. The dimensions were changed accordingly.
Once this was done we proceeded to start the machine operations.
CAM
Using VCarve
We need to define the toolpaths, add dogbones and tabs to the drawing so that the machine can cut them accordingly.
VCarve provides a powerful but intuitive software solution for creating and cutting parts on a CNC router.
The following steps were followed to make the cutting parts.
Reference point for drilling: We are supposed to drill the work piece on to the sacrificial layer so that it stays in place. If we blindly drill holes in random areas of the the job there is a chance that the screw may coincide with the toolpath. To avoid this from happening we run a drill path to mark refrence points for screwing the piece down. Create a few circles and place them on the edges where the paths dont meet.
Dogbones : Dogbones are made to give a good fit between the inner edges of slots. I added dogbones on all of my slots and edges.
Tabs: Tabs are added to give support to the cut parts which may move and cause issues when the tool . It can be quite dangerous if the tabs are not given appropriately.
Once the drill path and the toolpaths are given we can proceed to the operations. The entire operation process has been explained in detail in th e group project.